This research is directed toward the study of those substances that serve as synaptic transmitters in the CNS of Aplysia. One part of the program involves a dedicated search for specific neurons which contain high concentrations of those biogenic amines generally regarded as viable transmitter candidates and for which we have very sensitive micromethods. Previously identified acetylcholine-, serotonin-, and histamine-containing neurons have been shown by independent physiological and pharmacological studies to utilize these substances as synaptic transmitters. In addition, attempts will be made to identify neurons containing high concentrations of dopamine, octopamine, Gamma-aminobutyrate, and certain peptides. Another portion of the program is directed to the development of novel methods for the detection or characterization of transmitters which, by independent physiological and pharmacological criteria, do not appear to be any of the above candidates, nor are they likely to be amino acids, such as glycine, glutamate, or taurine. We will use the techniques of high performance liquid chromatography and gas chromatography-mass spectrometry to isolate and analyze cell constituents. To assess bioactivity, we will use the responses of the appropriate postsynaptic neuron to focal (pressure) application of purified tissue fractions, prepared either from individual neurons or from whole ganglia. Through these chemical studies we hope to identify new chemical substances serving as synaptic transmitters and the specific Aplysia neurons which use them. We believe this information is of fundamental importance and will be directly applicable to more complex nervous systems where combined chemical, physiological and pharmacological studies of individual neurons are not yet possible.